Piston rod



April 21, 1931.

C. SCHAER PISTON ROD Filed June 21. 1929 INVENTEJ R {M MM BY @wbw MM- $0M ATI'U RN Y.

. CHARLES SCHAER, OF/LANGENTHAIJ, SWITZERLAND; ASSIGNOR TO THE Patented Apr. 21, 1931 I omen s1:yrss PA ENT OFFICE Y SULZER- FRERES SQCIETE ANONYME, OFWINTERTHUR, SWITZERLAND rrs'ron ROD application filed Juli 21, 1929, S eria.1 No.

' This invention relates to piston rods of the kind through which a cooling medium circulated to the piston, for example, of a double-acting internal combustion engine. 1 The cooling medium, though primarily intended to cool the piston oisuch engines, cools the piston rod in passing through it and in this way the material from which the rod is" formed is exposed to severe heat stresses,"as the temperture of the inner fibres of the rod is considerably lower than that of the outer fibres. As a result,the outer parts of the rod tend toe'xpand to a greater extent'thanl the inner parts though the actual expansion assumes a'mean value midway between those of the inner and outer fibres of the rod. Hence the inner fibres are exposed to tension and the outer fibres to compression. t

The stresses thus produced assumeconsiderable dimensions over that portion of the piston rod which comes into contact with the very hot gases'in the lower working chamber of a double-acting internal combustion, engine. In the centre of the rod the temperature of the inner fibres may be say .7 0 C. and the outer fibres 120 C. and the difierence, 50 0., results in heat stresses which are still quite admissible. In that portion of the I piston rod nearest the piston, however, which is exposed to the highest temperatures, the outer fibres may be at as high a temperature as 300 C. and the temperature of the inner fibres not exceed 90 (3., giving a difference of 210 C. which produces ,very considerable heat stresses. V g V The object of the invention is to reduce to within admissible limits this difierence of temperature and the consequent heat stresses in such piston rods.

According to this invention the wall of the piston rod through which the cooling medium passes is reduced in thickness throughout that portion of its length which comes within the zone of the combustion chamber,

or throughout a portion of such length.

Various constructions according to the invention are diagrammatically illustrated in the accompanying drawings, in which Figure 1 is a vertical section through the cylinder of an internal combustion engine,

372,768, and vin Switzerland Iu1y 2, 1928.

showing the upper portion of the piston rod,

' Figures 2 to 7 are similar sectional elevations of modified constructions'of piston rod according'to this invention, and

Figure 8 is a cross-section of the illustrated in Figure 7 I In the double-acting internal combustion engine shown'in Figure 1,'the cylinder]. is furnished with an upper cover 2 and with a lower cover 3 through which passes the pis-' ton'ro d 5 of the piston 4:. In the lower cover is anannular'space 6 to receive the usual piston rod stufling box, and the piston rod is hollow and contains a pipe 8 through which cooling wa-T ter is supplied to the piston, discharge of this cooling water taking place through the bore 7. The lower section or length A of the pis ton rod has a bore of the diameter a, the s'ec tion or length B near the p'istonhaving a borel'of the diameter 1).

' In the construction shown in Figure 2, that.

portion of the; cooling water supply pipe '8 which lies within the widened portion of the bore, is thickened by having fitted to it an annular member ll ofaluminium or the like, secured to ,the pipe by soldering, riveting, screwing or in any other-suitable manner.

In'the construction shown in Figure 3, the supply pipe 8 is provided with a'widened portion 12, and in the modification shown in Fig- .ureg l the bore of the piston is widened at several points so as toform a number of internal circumferential ribs.

In Figure 5 an insulating pipe or sleeve 14 is provided extending over. the length of the widened portion of thebore. This. pipe may be formed ofheat insulating "material or the space between the inner wall ofthe .bore and the outer wall of'the pipe may ,be

' provided on'fthe' inner Wall of the bore throughout the widened portion thereof.

The widening of thebore of the piston rod according to the present invention increases the cooling action of the cooling medium on the outer fibres of the piston rod. Consequently the outer fibres of the rod will be at a temperature of say only 2005C. instead of 300 C. as hitherto, so that, assuming the temperature of the inner fibres to be 95 (3., the diflt'erence of temperature between the inner and outer'fibres will not exceed 105 C. The heat stresses in the piston rod will therefore be reduced-f about one-half of those which would exist if the bore of the piston rod were not widened; I

The use of, the throttling member shown in Figure 2 increases the speed of the cooling medium in the region where the piston-wall thickness is reduced, so that the Walls of the piston red are more rapidly cooled where their thickness is reduced, and the same effect can be obtained by the arrangement illustrated in Figure 3. ,7

Z In the construction shown in Figure 4, the coolin surface of the inner wall of the piston ref 5 is increased and the cooling medium is forced to assume an eddying flow throughout the length provided with ribs 13. Both these factors increase the transmission of heat from the piston rod to the cooling medium. 1

In the construction illustrated in Figure 5, the insulating sleeve or pipe 14 prevents the cooling medium from coming into contact with the wall of the piston rod over the widened portion of its bore, and hence the wall of the rod 5 opposite the sleeve 14 will be at a higher temperature, but the difference of temperature between the inner and outer fibres will be less than is the case if the cooling water'is allowed direct access against the inner wall of the widened bore, a reduction in heat stresses being thus ensured.

In the construction shown in Figure 6, the coolin medium is forced to follon a helical path t 11011 h the conduit 15 and is thus conveyed deep y into the walls of the piston rod. In Figures 7 and 8 the longitudinal ribs16 further serve to strengthen the rod and increase the area acted upon by the cooling medium. 1 e

In principle; that portion of the piston rod 'which comes into contact with the hot gases of the'lower combustion chamber is furnished with a widened bore 9, and the desired result can'be obtained in various ways. Thus, the section B over which the piston bore is widened could be increased or reduced, and instead of the cooling medium being supplied through the pipe 8 and discharged through the annular passage 7 the latter may be used to supply, dischar e being permitted to take place throng the .pipe 8.

Satisfactory working conditions can be obtained if the diameter Z) of the widened bore 9 is equal to or greater than half the diameter of the piston rod, so that the thickness of the remaining wall of the piston rod throughout the widened portion is a quarter or less of the diameter of the piston rod.

I claim:

1. In a double-acting internal combustion engine, a piston rod having an axial bore therein to permit the flow of a cooling medium therethrough, the wall of said bore being of lesser thickness over at least a portion of the length of the rod entering the cylinder than over the remaining length of the rod.

2. Apparatus according to claim 1 including means for increasing the heat transfer from the outer surface of the rod at the portion of the wall having a reduced thickness, said means being provided in the bore adjacent said portion of the wall.

3. Apparatus according to claim 1, wherein ribs are provided on the inner surface of the portion of the wall having a reduced thickness.

4. Apparatus according to claim 1, including means for increasing the rate of flow of the cooling medium over the portion of the wall having a reduced thickness, said means comprising a throttling member disposed in the bore adjacent said portion of the wall.

5. Apparatus according to claim 1, including means for deflecting the flow of cooling medium in its passage through the section of the bore adjacent the port-ion of the wall having a reduced thickness.

In testimony whereof I have afiixed my signature.

CHARLES SOHAER. 

